They expel their zooanthellae which gives them that highlighter look. Corals for the most part rely on zooanthellae to provide them with the nutrition to sustain them and grow. The colors that you see on the coral tissue is from the zooanthellae. Most of the light pinks that you see are bleached and will eventually die and even if they don't once they recover their zooanthellae, they end up looking a different color (that hi-lighter pink mushroom is most likely either brown or orange originally).